Math is good for you.
2 parallel coils means 4 coils.
Your wattage is therefore split 4 ways - Even though it doesn't quite work out that simply.
So here's some numbers on your .4 ohm build.
30 watts = reduced watts runing through each resistance wire, resulting in a pretty lackluster 3.46 volts, which is lower than native battery output at full charge.
50 watts = this comes out to 4.47 volts, which it running pretty hot, especially with the twist. It's about the top end I'd suggest for anything but a dripper, and you're gonna cook the juice off pretty fast.
100 watts = 6.32 volts - cloud chasing flavor destroying territory. Not saying it's wrong, saying that you'll probably spend more on juice than you did on cigarettes... but the 100 does give you the ability to have the most head-space above your casual vaping settngs....